1. Field of the Invention
The invention is directed to an adjustable damping valve which permits the degassing of the damping medium.
2. Description of the Related Art
In a vibration damper with hydraulic damping medium, it must be ensured as far as possible already during assembly that no air becomes trapped in the vibration damper. Air can become trapped due to the design of the structural component part. Gas can be dissolved in the hydraulic damping medium to a limited extent so that the damping medium consists of a hydraulic phase and a gaseous phase. If the volume fraction of the gaseous phase were constant, then the vibration damper could be designed for this boundary condition. However, the trapped air, which constitutes a purely gaseous phase, could be additionally dissolved in the damping medium. The damping medium is then made up of a liquid phase and a gaseous phase. Further, the purely gaseous phase can be entrained by the damping medium. Accordingly, the gaseous phase dissolved in the damping medium and the gaseous phase are distributed over the flow paths in the vibration damper. The dissolved gaseous phase can be separated from the damping medium due to a change in the temperature level and/or pressure level and then likewise presents a purely gaseous phase. The purely gaseous phase can collect in an area of the vibration damper as a bubble, or free gas as it is called hereinafter, and be present, e.g., at a functional surface which is acted upon by pressure as part of a functional space of the vibration damper. The gas present in the functional space alters the damping function. When the vibration damper is constructed based on the twin-tube principle, a piston rod guiding and sealing unit is often used so that gas which is trapped in the damping medium can escape from a work space into a compensation space via the piston rod seal.
Further, it is known to provide a degassing channel in an adjustable damping valve to produce a connection between an interior space of the adjustable damping valve and a work space. The cross section of the connection is small enough to allow degassing of the damping valve without any damping medium escaping. However, a connection of this kind is difficult to produce and to implement with respect to construction.
If possible, the adjustable damping valve is arranged in or at the vibration damper in such a way that any gas bubbles rise out of the damping valve and can escape into a work space. However, this particular installation position is not always possible, e.g., because a power supply line for an actuator of the adjustable damping valve calls for a particular installation position of the adjustable damping valve.
The trapped gas becomes noticeable particularly when the hydraulic pressure on a surface of a valve body is used to adjust the damping valve. The trapped gas leads to a certain compressibility of the damping medium and, therefore, to a change in the dynamic operating behavior of the adjustable damping valve. Although the desired hydraulic force components are achieved at the component parts of the valve which determine the damping force characteristic, the compressibility of the damping medium leads to an unwanted and undefined delay in the buildup of these force components. In terms of a static view of the error, a bogus adjusting force is briefly applied to this valve part.
It is thus an object of the present invention to overcome the problem associated with free gas known from the prior art.